Equivalent slab thickness at the mid-latitude ionosphere during solar cycle 23

Abstract

The shape of the vertical electron density profile reflects the complexity of production, loss and transportation of plasma in the Earth’s ionosphere. A first order measure of the profile shape is the equivalent slab thickness which is defined as the ratio of the total electron content TEC and the ionospheric peak density NmF2. This ratio is very sensitive to the competition of plasma driving forces such as thermospheric winds and electric fields. Hence, this parameter is very helpful in exploring perturbation processes in the ionosphere. To get near real time information on these perturbation processes, the equivalent slab thickness is continuously monitored by combining vertical sounding and corresponding TEC data over Juliusruh /Germany since the beginning of 2009 via the space weather service SWACI (http://swaciweb.dlr.de). Monitoring results are discussed and compared with long-term studies based on TEC and ionosonde measurements covering the entire solar cycle 23. Whereas the slab thickness is well correlated with thermospheric heating at daytime the slab thickness increases significantly due to the enhanced contribution of the plasmasphere to TEC in the night. We firstly report a correlation study of the equivalent slab thickness with the equivalent slab thickness of the bottomside ionosphere. The bottomside slab thickness is derived from radio occultation measurements onboard CHAMP within the time period 2001 -2009, thus covering high and low solar activity conditions. Based on the comparison of both parameters we discuss the ratio between bottom- and topside ionosphere under quite different geophysical conditions.